Message-ID: <50588450.9090709@opinioni.net>
Date: Tue, 18 Sep 2012 16:25:20 +0200
From: Andrea Suisani <sickpig@opinioni.net>
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To: Merlin Moncure <mmoncure@gmail.com>
CC: pgsql-performance@postgresql.org
Subject: Re: 20% performance drop on PostgreSQL 9.2 from kernel
	3.5.3 to 3.6-rc5 on AMD chipsets
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[cut]

>>>> Kernel config - http://pastebin.com/cFpg5JSJ
>>>>
>>>> Any ideas?
>>>
>>>
>>> Did you tell LKML? It seems like a kind of change that could be found
>>> using git bisect of Linux, albiet laboriously.
>>
>> just a pointer to LKML thread:
>>
>> https://lkml.org/lkml/2012/9/14/99
>
> There's some interesting discussion of postgres spinlocks in the thread:
>
> "Yes, postgress performs loads better with it's spinlocks, but due to
> that, it necessarily _hates_ preemption."

another one:

https://lkml.org/lkml/2012/9/15/39

quoting the relevant piece:

On Sat, Sep 15, 2012 at 06:11:02AM +0200, Mike Galbraith wrote:
 > My wild (and only) theory is that this is userspace spinlock related.
 > If so, starting the server and benchmark SCHED_BATCH should not only
 > kill the regression, but likely improve throughput as well.

after that message Borislav Petkov tried to
to exactly that using schedtool(8) (tool to query and set CPU
scheduling parameters)

and he can confirm that performace are "even better than the results with 3.5
(had something around 3900ish on that particular configuration)."


Andrea